but I have a problem because the date displaied are all wrongs (like Sep 11, 40014, 7:40 am)
I use Json lib to serialize a java Date object and I test the conversion for date (yyyy-mm-dd hh:mms): 2008-01-17 13:56:30.0 becomes serialized in 1200574590000.
In another example for Json in Ext forum I see a format like this "lastpost":"1200320864"
Is there another configuration for dateFormat: 'timestamp' to parse correctly the date field ?
Thanks a lot for all help

You still need a dateFormat, but that's just for the output of the data, it arrives in Javascript as a fully instantiated Date object with no need for any parsing.

After test I understand "timestamp" format is equals to "U" format (I do not find "timespamp" everywhere) and I modified Json lib to have date in seconds format instead millisecond like standard for javaa.
Thanks a lot Animal for help